1. Field of the Invention
The present invention relates to a hermetic seal cover to be used in hermetically sealing a package for various electronic parts.
2. Description of the Related Art
Semiconductor devices such as SAW filters and quartz oscillators, which are used in various electronic appliances for, for instance a cellular phone are normally used with the devices enclosed in a ceramic-made container (package), which prevents oxidation or deterioration due to moisture or oxygen. The semiconductor package comprises: a container (base), which has openings and hermetically seals devices; and a seal cover acting as a lid. A process for hermetically sealing a semiconductor package is effected through placing semiconductor devices on a base, placing a seal cover on the devices, and subsequently joining the base and the seal cover.
A typical method out of various ones for joining a base and a seal cover is a brazing method, in which joining is effected with the use of brazing materials. A seal cover to be used in the brazing method has on a joint surface thereof brazing materials fusion-bonded, and in hermetic sealing, the seal cover is allowed to cover the base, and the seal cover and the base are heated by the use of any heating means including an electric furnace to melt and solidify the brazing materials for completing a package.
It should be noted that, as constituent materials for a seal cover main body, KOVAR (Fe—Ni—Co alloy) and 42 Alloy (Fe—Ni alloy) are generally used. As a brazing material, a Au—Sn brazing material is used for the good reason that it is excellent in reliability and corrosion resistance. Especially, the generally used is a Au80 wt %-Sn20 wt % brazing material, which has an eutectic structure. In a manufacturing process of the seal cover, the seal cover main body is subjected to Ni plating and/or Au plating for insuring both corrosion resistance of the seal cover and wettability of molten Au—Sn brazing material, and Au—Sn brazing material is allowed to join to form a seal cover. Such joining of Au—Sn brazing material is effected though for instance fusion or pressure welding. Japanese Patent Application Laid-Open No. 2003-142615 is a document, which discloses a method of manufacturing a seal cover through pressure welding of a brazing material.
When a seal cover is joined to a base in manufacturing a semiconductor package, nondefective joining is demanded for insuring production yield. The above-mentioned joining with the use of a conventional seal will offer good joining basically, however voids generate at the joint on very rare occasions.
A rejection rate of products due to the defect is of the order of 1-2% of the entire products, which is small by ratio. However, the number of semiconductor packages mass produced with the popularization of various electronic equipment is quite a few even if the proportion is small, and a loss suffered thereby should not be left disregarded.